Influence of methodology on the presence and extent of mismatching betweenTc-99m-MIBI and I-123-BMIPP in myocardial viability studies

Discordant uptake (mismatching) of I-123-labeled beta-methyl-p-iodophenyl-p entadecanoic acid (BMIPP) less than Tc-99m-labeled methoxyisobutyl isonitri le (MIBI) is a good predictor of myocardial viability. However, methodologi cal factors can influence assessment of the presence of mismatching because of differences in background activity between the tracers. In this study, we investigated the influence of methodological parameters on the mismatchi ng between BMIPP and MIBI in patients with chronic ischemic heart disease. Methods: Polar maps were created to quantify the extent of mismatched tissu e measured in 10 patients with myocardial infarction according to three met hods for data processing: no correction, subtraction of background activity measured in the left ventricle cavity and dual-window scatter correction. Mismatching was expressed as a percentage of the surface of the left ventri cle globally as well as for each arterial territory using a BMIPP uptake of at least 10% less than MIBI as the threshold. The results of dobutamine st ress echocardiography and the evolution of the regional contractility at 6- mo follow-up were used as references. Results: Mean background activity in the ventricle cavity was 9.3% of the maximum activity for MIBI and 21.4% fo r BMIPP before, and 2.8% and 8.3% after scatter correction. Fourteen arteri al vascular territories demonstrated baseline wall-motion abnormalities; 9 territories showed contractile reserve with dobutamine stress echocardiogra phy. Significant mismatching was found in 5 of 14 regions without correctio n, 9 of 14 after scatter correction and 13 of 14 after background subtracti on. Compared with the evolution of resting regional contractility at follow -up, optimal results were found when using the scatter-corrected data. With out correction, mismatching between BMIPP and MIBI was partially disguised because of the higher noise level in the iodine images. On the contrary, su btraction of background measured by means of a single region of interest ov erestimated the magnitude of mismatching due to the heterogeneous backgroun d distribution in the ventricular cavity. Conclusion: In quantifying the pr esence and extent of mismatching between MIBI and BMIPP in chronic ischemic heart disease, significant differences in the detection of viability are n oted according to the acquisition and processing methods used. Scatter corr ection of the acquisition data is the most accurate and reliable method for identifying viable myocardium.